Sliding sleeves valves provide selective access outside a tubing string for a variety of applications. One popular application is for formation access for fracturing. In the past these sliding sleeves were shifted in a variety of ways in a fracturing application. The sliding sleeves could have integral ball seats that get progressively larger from further downhole and in an uphole direction. The fracturing proceeded from bottom up and each time a bigger ball was dropped to land on the next higher sliding sleeve while isolating any previous sleeves shifted open in the same manner. When the fracturing is complete the well is put on production and the theory is that the balls on the seats are simply carried up to the surface past all the seats above their original location. This does not always happen and logjams can occur that can impede subsequent production.
As an alternative to using ball seats of gradually increasing size from well bottom to the surface a different shifting technique has been developed. One such device is the Multi-stage Unlimited Frac Isolation System from NCS Energy Service Inc. which combines a locator for finding the sliding sleeve with a bottom hole assembly and a resettable packer that can be set against the sleeve. Pressure is applied with the packer against the sleeve and the sleeve shifts to open a wall port. A ported sub is opened in the coiled tubing string and the fracturing fluid is delivered through the annulus to the port opened by the shifted sliding sleeve while the coiled tubing can be used as a dead string to measure fracturing pressure or it can be used to circulate or reverse circulate in the event of a screenout. An animation of this system is available on the NCS website.
One issue with this system is that the acceleration and abrupt deceleration of the sliding sleeve as it hits a travel stop has created stress failures in the coiled tubing or related fittings adjacent the packer that grabs the sliding sleeve. These failures have brought about a proposed solution for a shock absorber for the sliding sleeve that crumples a bellows on travel stop impact as illustrated in US Publication 2009/0266659. A related crumpling type shock absorber for a dropped string in a hole is shown in U.S. Pat. No. 7,779,907. There are limitations to the crumple design for a sliding sleeve and those are that the drift diameter is reduced from the crumpling so that travel of other tools past a sliding sleeve could be impeded and that the crumpling may stick the sleeve in the position before it is fully shifted or prevent the sleeve from being shifted in the reverse direction should there be a need to close the port with the sliding sleeve.
Other applications for shock absorbers have involved annular rubber rings that simply get compressed and bounce back after the shock loading is removed. These have been used in sliding sleeves that are closed with a mechanical shifting tool such as item 104 in FIG. 11 B of U.S. Pat. No. 5,549,161. On a much larger scale large annular rubber shapes have been used on jack-up rig legs such as item 46 in U.S. Pat. No. 4,195,950. Of general interest as to sliding sleeves is U.S. Pat. No. 7,108,067.
What is needed and provided by the present invention is a hydraulic shock absorber for a sliding sleeve that does not reduce drift and that addresses the stress failure in the coiled tubing and associated components from shock loading at the end of the movement of the sliding sleeve. Those skilled in the art will better understand additional aspects of the present invention from a description of the preferred embodiment and the associated drawings with the understanding that the full scope of the invention is given by the appended claims.